1. Field of the Invention
The present invention relates to a method and an apparatus for driving a plasma display panel (PDP). More particularly, it relates to a plasma display panel driver that reduces the occurrence of a dynamic false contour by dividing scanning lines into two or more groups and sustaining according to different ratios.
2. Description of the Related Art
Referring to FIG. 1, where a schematic diagram of the conventional methods of driving a plasma display panel is shown, a frame-display operation is composed of a plurality of subframe-display operations. For example, one frame picture in a plasma monitor with 256 gray levels includes eight subframes SF0xcx9cSF7 as shown in FIG. 1. Each subframe-display operation is completed by the following three steps of resetting, scanning, and sustaining. In a full frame-display operation, the working periods of the reset operation and the scan operation in the subframe-display operation are the same. In the case of 256 gray levels, the ratio of the working periods of the eight sustain steps can be assigned to 1:2:4:8:16:32:64:128:256. Thus, the plasma display panel is driven and shows 256 gray levels.
In a plasma display panel with 256 gray levels, the working period of the sustain operation is in proportion to the brightness level of the plasma display panel. Accordingly, when eight bits represent each pixel in the plasma display panel, the eight working periods of the sustain operation in a frame-display operation correspond to the eight bits, respectively. The longest working period of the sustain operation corresponds to the highest bit, and the shortest working period of the sustain operation corresponds to the lowest bit. As described above, the ratio of the working periods of the eight sustain operations can be assigned to 1:2:4:8:16:32:64:128. That is the working periods of the sustain operation correspond to the eight bits of a pixel, respectively. In order to adjust the brightness level of the plasma monitor and improve the effect for displaying, the working period of the sustain operation can be set to other ratios.
However, there can exist continuous colors in an area when one frame picture switches to another frame picture. That is, the color level and the brightness level of a first frame picture displaying before may he close to that of a subsequently displayed frame picture. Therefore, there might be a dynamic false contour in the plasma display panel. Further, tho area displaying the dynamic false contour might display an uncommon continuous dark area or an uncommon light area. For example, in a frame-display operation of a plasma display panel with 256 gray levels, the ratio of the working periods of the eight sustain operations are assigned to 1:2:4:8:16:32:64:128. It is supposed that a pixel is represented by eight bits. When the analog value of the eight bits is below and close to 127, the pixel is mainly sustaining and producing brightness in the prior seven subframe-operations. When the analog value of the eight bits is above and close to 128, the pixel is sustaining and producing brightness in the eighth subframe-operation. As colors with continuity probably exist in an area (or a block) when one frame picture switches to the other frame picture, a serious dynamic false contour may occur. For example, the analog value representing the intensity of colors and the brightness of a block A is below 127(and close to 127), while the analog value representing the intensity of colors and the brightness of a block B is above 128 (and close to 128) When the block A switches to the block B, an uncommon dark area is shown. Conversely, when the block B switches to the block A, an uncommon light area is shown.
FIG. 2A schematically shows the conditions when the block A switches to the block B, while FIG. 2B schematically shows the conditions when the block B switches to the block A. In FIG. 2A and FIG. 2B, the horizontal coordinate represents the period of time passed, i.e. the frame (n), frame (n+1), frame (n+2) . . . . Further, the white block represents block A and the block with cross lines represents the block B. Referring to FIG. 2A, where the analog value representing the intensity of colors and the brightness of a block switches from 127 to 128 is shown. Because eight dark subframes continuously appear in the frame picture, the dynamic false contour is caused. Also, FIG. 2B shows the analog value representing the intensities of colors and the brightness of a block switches from 128 to 121. Because eight light subframes continuously display, the dynamic false contour appears.
Accordingly, in order to reduce the dynamic false contour, some methods have been developed. For example, the times those dynamic false contours occur are counted. Based on this, the ratios or orders of sustaining in the eight subframes are amended. However, the method is effective on specific frame pictures. In other words, it is no use on other frame pictures.
In order to solve the problems described above, the primary object of the invention is to provide a method and an apparatus of driving of a plasma display panel reducing the dynamic false contour, wherein the plasma display panel is composed of a plurality of scanning lines, and a subframe is completed by three steps of resetting, scanning and sustaining, while a full frame picture is composed of a plurality of subframe-display operations, wherein the subframe-display operations in the full frame picture sustains according to a predetermined ratio so that a plurality of gray levels are obtained.
According to a second embodiment of the method of the present invention, the scanning lines are divided into a plurality of groups, and the subframe-display operations of groups of scanning lines sustain according to the predetermined ratio with different orders in the full frame picture. If, example, the full frame picture is composed of eight subframes-display operations to obtain 256 gray levels, the subframe-display operations of the first group sustain according to an order of 1:2:4:8:16:32:64:128 in the full frame picture, and the subframe-display operations of the second group sustain according to an order of 128:64:32:16:8:4:2:1 in the full frame picture.
Furthermore, the present invention provides a driving circuit of a plasma display panel to reduce dynamic false contour. The scanning lines of the plasma display panel are divided into a first group and a second group. In addition, the scanning lines have respectively a scanning electrode and a sustaining electrode. The driving circuit includes a data driver, a first scan driver, a second scan driver, a first sustaining driver, a second sustaining driver, and a timing controller. The data driver is used to receive the data displayed on the plasma display panel. The first scan driver is used to read the data displayed on the plasma display panel, and outputs tho data of the first group to the scanning electrode of the first group according to a first order or ratio. The second scan driver is used to read the data displayed on the plasma display panel, and outputs the data of the second group to the scanning electrode of the second group according to a second order or ratio. The first sustaining driver connects to sustaining electrodes of the first group, while the second sustaining driver connects to sustaining electrodes of the second group. In addition, the timing controller controls the timing of the first scan driver, the second scan driver, the first sustaining driver, and the second sustaining driver to drive the plasma display panel.